1. Field of the Invention
The present invention relates generally to semiconductor laser devices, and more particularly, to a single mode semiconductor laser device having an insulation region in place of a grating.
2. Description of Related Art
The technology employing semiconductor optical component (semiconductor laser) as optical communication component is originated in the 80's in Bell laboratories. Nowadays, the study is more concentrated on how to make the semiconductor optical component (i.e. semiconductor laser) exert the capability of high-speed carrier signal and long-range transportation. Based on such application, the capability of the basic transportation signal according to the semiconductor laser component is all through the task continuously researched in such industry. In the conventional laser diode, its optical cavity is paralleled with epitaxial layer, the reflecting surface is formed after plating the reflecting mask on the crystal natural fracture surface and plumed with the epitaxial layer, the ray between both sides of the mirror surface of the active region reflects back and forth, then produces multi-mode laser ray from the side.
In present optical communication system, the pursuit of high speed and large capability has become the eternal target in the development of optical communication, single mode laser component is produced conforming to the demand, and among many features of the semiconductor laser, the single mode spectrum output which determines the distance of the signal transportation is one of the most important features of the semiconductor laser.
In order to form laser with single output wavelength, nowadays, grating integrated in the semiconductor laser component is mostly adopted in such industry, so that single mode laser is formed through the optical output with certain wavelength by the frequency selection function of the grating. For example, U.S.A. Publication No.20030169792 proposed a DBR Distributed Bragg Reflector (DBR) laser, with reference to FIG. 1. The DBR laser comprises a first grating section 220, a second grating section 240, an active section 230, a first cladding layer 120, a second cladding layer 180, a first waveguide layer 140, a second waveguide layer 160, an active layer 130, a first top electrode 190, a second top electrode 200, a third top electrode 210, and a bottom electrode 110.
The first cladding layer 120 is an n-type InP substrate. The bottom electrode 110 is formed on a bottom surface of the first cladding layer 120. The second cladding layer 180 is a p-type InP substrate.
The active layer 130 is formed on the active section 230. When an electric field is applied to the active section 230, electrons in the active section 230 will be drifted from the first cladding layer 120 to the active layer 130, and holes in the active section 230 will be drifted from the second cladding layer 180 to the active layer 130. The electrons and holes drifted to the active layer 130 are combined to form optical signals.
The first waveguide layer 140 is formed in the first grating section 220 and is disposed on one side of the active layer 130. A plurality of first gratings 150 are formed on a top surface of the first waveguide layer 140. Optical signals traveling from the active layer 130 onto the first waveguide layer 140 and having a first predetermined wavelength are allowed to pass through the first gratings 150, which is capable of performing a frequency selection function.
The second waveguide layer 160 is formed in the second grating section 240 and disposed on another side of the active layer 130. A plurality of second gratings 170 are formed on a top surface of the second waveguide layer 160. Optical signals traveling from the active layer 130 onto the second waveguide layer 160 and having a second predetermined wavelength are allowed to pass through the second gratings 170, which is also capable of performing the frequency selection function.
The first top electrode 190, the second top electrode 200 and the third top electrode 210 are all formed on the second cladding layer 180, and disposed in the first optical grating section 220, the active section 230 and the second grating section 240 respectively.
The DBR laser can produce single mode laser ray by employing grating to filter, and achieve the purpose of tuning the output optical wavelength by adjusting the electric field density produced between the first top electrode 190, the second top electrode 200, the third top electrode 210 and the bottom electrode 110, thereby the structure, design and fabrication of the grating is key quality of the. But it is need to use high fabrication precision to filter in the DBR laser, and the grating fabricating process is complex, so that the fabricating process of the DBR laser becomes complex, the time of the fabricating process and the cost of the fabricating process increase, meanwhile, due to the requirement for the extremely high precision of the grating, the fabricating time to yield of the semiconductor laser with grating correspondingly reduces, furthermore, the purpose of tuning the output optical wavelength can not be achieved, unless the power supply is simultaneously imposed on the first top electrode 190, the second top electrode 200 and the third top electrode 210, and the size of the semiconductor laser increases because the grating is integrated in the semiconductor laser, thus, such laser could not conform to the micromation development tread of the present electronic products and the requirement for continually upgrading the features.
American Patent Publication No.4622471 further proposes a multicavity optical device, which makes the principle of coupling the cavity with the laser apply in the semiconductor laser to produce single mode laser ray, but the device can not tune the output optical wavelength, and the first laser region and the second laser region of the device are unattached, single mode laser could not be produced until the power supply is simultaneously imposed on the first and second laser regions, furthermore, the first and second laser regions in the device are mounted on the surface of the substrate through the SMT (Surface Mounting Technology) fabrication, and single mode laser with good performance can not be produced until the relative position of the first and second laser regions is extremely accurate, so that the difficulty degree and the cost of the fabricating process increase.
American Patent Publication No.6978057 further proposes an optical waveguide and a method for providing an optical waveguide. A laser diode (1) having an optical path (15) defined in an active layer (2) which is sandwiched between a substrate layer (3) and a top layer (4) and defined by a ridge (14) formed in the top layer (4) outputs laser light of a single predetermined wavelength. Refractive index altering grooves (21) extending transversely in the top layer (4) are provided at spaced apart locations for altering the refractive index of the active layer (2) along the optical path at partial reflecting locations (20) for causing partial longitudinal reflections of the laser light generated in the optical path (15) so that standing waves or harmonics thereof of the single predetermined wavelength are set up between the respective partial reflecting locations (20) and a first mirror facet (8) in the optical path (15). In order that the standing waves set up between the partial reflecting locations (20) and the first mirror facet (8) are harmonics of the predetermined single wavelength, the refractive index altering grooves (21) are located along the ridge (14) for forming the reflecting locations (20) at distances from the first mirror facet (8) which correspond to the effective length of the optical path (15) resulting from the affect of the inclusion of the reflecting locations (20) rather than at locations corresponding to the actual length of the light path (15).
Accordingly, there exists a strong need in the art for a semiconductor laser device to solve the drawbacks such as complex fabricating process, low fabricating time to yield and high cost caused by the conventional technology employing grating, and the drawbacks such as the complicated fabricating process and the increasing cost caused by the conventional technology which could not tune the output wavelength.